Fossils of a meter-long (3.3-foot) prehistoric ocean predator have been found in southeastern Morocco.

The specimens comprise the largest yet of its kind and suggests the spiny, somewhat shrimplike beasts dominated pre-dinosaur seas for millions of years longer than thought.

Previous anomalocaridid fossils had shown the animals grew to perhaps 2 feet (0.6 meter) long, which previously would have made them the largest animals of the Cambrian period (542 to 501 million years ago)—an evolutionarily explosive time, when invertebrate life evolved into many new varieties, such as sea lilies and worms.

The new anomalocaridid fossils also gave scientists another surprise: They're surprisingly young. Dating back to "only" 488 to 472 million years ago, in the Ordovician period, the specimens hint that anomalocaridid species survived for 30 million years longer than earlier evidence had suggested.

Anomalocaridids are widespread in fossils from the Cambrian, "then they depart from the rock record at about 510 million years ago," said Briggs, who received funding from the National Geographic Society's Committee for Research and Exploration.

Eventually, though, anomalocaridids did go wiped out—leaving no modern descendants, Briggs said. "It most probably was ultimately replaced by fishes or other kinds of predators in later oceans," he said.